This invention relates to optical devices, and more particularly to optical waveguide devices.
In the integrated circuit industry, there is a continuing effort to increase device speed and increase device densities. Optical devices are a technology that promise to increase the speed and current density of the circuits. Interferometers, such as a Michelson interferometer, measure distances or relative motions of objects using light. Interferometers can be formed from multiple passive elements, with each passive element made from glass or clear plastic or alternatively from a semiconductor material, such as silicon.
Interferometers, as with most optical devices, are delicate optical systems that are susceptible to changes in such operating parameters as temperature, device age, device characteristics, device age, device characteristics, contact, pressure, vibration, etc. As such, the various components of the interferometers are typically contained in packaging that maintains the parameters as desired. Providing such packaging is extremely expensive. Even if such packaging is provided, passive interferometers may be exposed to slight condition changes. Passive interferometers perform differently under different conditions. For example, different bandwidths of light will be attanuated to different levels depending on the conditions. If the characteristics of a passive interferometer is altered outside of very close tolerances, then the optical interferometer will not adequately perform its function. In other words, there is no adjustability for passive interferometers.
As such it would be desirable to provide an optical interferometer that can controllably measure distances or motions using one or more light bandwidths. Additionally, it would be desirable to provide a mechanism to compensate in interferometers for variations in the operating parameters such as temperature and device age.
The present invention is directed to an optical interferometer apparatus and associated method including a beamsplitter, a first mirror, a second mirror, and a delay element. The beamsplitter splits an input optical signal into a first optical signal that flows along a first optical path and a second optical signal that flows along a second optical path. The first mirror reflects the first signal in the first path towards the beamsplitter to form a first return path. The second mirror reflects the second signal in the second path towards the beamsplitter to form a second return path. The delay element includes the first mirror that adjusts a time required for the first signal to flow along the first path, the delay element comprises a waveguide, a first electrode, a second electrode, and a two-dimensional electron (hole) gas (2DEG). The waveguide includes a region of changeable propagation constant disposed along a length of the waveguide, wherein the first optical signal is guided by total internal reflection in the waveguide. The waveguide is formed at least in part from an active semiconductor. The first electrode is positioned proximate a first surface of the region of changeable propagation constant and electrically separated from the active semiconductor. The second electrode is in electrical contact with the active semiconductor and disposed on a first side of the region of changeable propagation constant. The 2DEG has a free carrier distribution that is formed on the first surface of the active semiconductor when a voltage is applied between the first electrode and the second electrode. Changing the voltage causes a corresponding change of the free carrier distribution which, in turn, causes corresponding change of a propagation constant level in the region of changeable propagation constant that changes the time required for light in the first optical signal to flow along the first path.